The present invention is directed toward semiconductor processing technology and, in particular, to the use of titanium nitride (TiN) layers with tungsten plugs in vias to make interlayer connections.
Present-day, high-performance integrated circuits typically have multiple layers of metal conducting lines. These metal layers are separated by thick, silicon dioxide insulating layers. Vias are made through the insulating layers to make connections between the metal lines. It is often desirable that the metal conducting lines be maintained in as much of a plane as possible to avoid undue stresses on the metal lines. A tungsten metal plug is often used to fill the via, or contact hole, in the insulating layer covering a first metal line so that the overlying metal layer from which a overlying second metal line is formed remains on the planar surface of the insulating layer. Without the plug, the overlying metal layer must dip into the via to make contact with the underlying first metal line.
A layer of titanium (Ti) is typically placed in contact with the underlying first metal line to facilitate the formation of controllable low ohmic contacts. As the Ti layer is very reactive, a layer of titanium nitride (TiN) is placed in contact with the plug as a reactive barrier layer between the tungsten and the Ti layer. For example, if the underlying first metal is aluminum, a Ti layer is conventionally placed on the aluminum layer, followed by a TiN layer, and then the tungsten layer. The Ti layer also acts as a "glue" between the insulating layer and the TiN layer.
Heretofore, it has been believed that the TiN layer should be formed to a fair thickness (approaching 1000 .ANG. and more) to act an effective barrier. The present invention is based, to the contrary, that an effective TiN barrier is created with a thin layer, 100 .ANG. and even less. With the present invention, a TiN processing step is simplified with increased throughput and reliability of the TiN layer.